Charlie Chan’s Secret is the tenth Fox-produced film in the Charlie Chan series with Warner Oland as the detective.

Plot:
Alan Colby, heir to a vast fortune, reappears after a seven-year absence, only to be murdered before he can claim his inheritance. The Lowells have been living off the Colby fortune, and now someone is trying to kill Henrietta Lowell, matriarch of the family. Among the suspects are:

Fred and Janice Gage, who live off the Lowell (Colby) fortune, which would have gone to Alan Colby, the murdered man
Prof. Bowen, who is paid handsomely by the Lowells for his valuable psychic research
Mr. Phelps, the executor of the Lowell estate
Ulrich, the caretaker who had a longstanding grudge against Alan Colby
Henrietta Lowell, the aunt of Alan Colby who wants to continue psychic research.

Charlie Chan is called to investigate Alan Colby’s murder where clues include:

A clock deliberately set to the wrong time
The old house has secret passageways
A medieval dagger used to commit the murder
A rifle rigged to fire by itself